In general the function of a circuit breaker is to electrically engage and disengage a selected circuit from an electrical power supply. This function occurs by engaging and disengaging a pair of operating contacts for each phase of the circuit breaker. The circuit breaker provides protection against persistent overcurrent conditions and against the very high currents produced by short circuits. Typically, one of each pair of the operating contacts are supported by a pivoting contact arm while the other operating contact is substantially stationary. The contact arm is pivoted by an operating mechanism such that the movable contact supported by the contact arm can be engaged and disengaged from the stationary contact.
There are two modes by which the operating mechanism for the circuit breaker can disengage the operating contacts: the circuit breaker operating handle can be used to activate the operating mechanism; or a tripping mechanism, responsive to unacceptable levels of current carried by the circuit breaker, can be used to activate the operating mechanism. For many circuit breakers, the operating handle is coupled to the operating mechanism such that when the tripping mechanism activates the operating mechanism to separate the contacts, the operating handle moves to a fault or tripped position.
To engage the operating contacts of the circuit breaker, the circuit breaker operating handle is used to activate the operating mechanism such that the movable contact s) engage the stationary contact s). A motor coupled to the circuit breaker operating handle can also be used to engage or disengage the operating contacts. The motor can be remotely operated.
A typical industrial circuit breaker will have a continuous current rating ranging from as low as 15 amps to as high as 160 amps. The tripping mechanism for the breaker usually consists of a thermal overload release and a magnetic short circuit release. The thermal overload release operates by means of a bi-metalic element, in which current flowing through the conducting path of a circuit breaker generates heat in the bi-metal element, which causes the bi-metal to deflect and trip the breaker. The heat generated in the bi-metal is a function of the amount of current flowing through the bi-metal as well as for the period of time that that current is flowing. For a given range of current ratings, the bi-metal cross- section and related elements are specifically selected for such current range resulting in a number of different circuit breakers for each current range.
In the event of current levels above the normal operating level of the thermal overload release, it is desirable to trip the breaker without any intentional delay, as in the case of a short circuit in the protected circuit, therefore, an electromagnetic trip element is generally used. In a short circuit condition, the higher amount of current flowing through the circuit breaker activates a magnetic release which trips the breaker in a much faster time than occurs with the bi-metal heating. To limit the duration and the intensity of short circuit currents, the circuit breaker must, within the shortest possible time, separate its contacts and extinguish the resulting electric arcs. The circuit breaker must operate to shorten both the time of intervention, i.e., commence movement of the contacts away from each other and the time of extinction of the arc by increasing arc voltage. The known manner to extinguish the arc is to extend it and cool it. Prior art methods have included puffing air or a gas into the arc chamber while the contacts of the circuit breaker move apart. Another solution has been to install a magnetic motor which forces the arc in a selected direction typically into a stacked array of arc baffels. A further solution has been to increase the number of baffels in the stacked array and insert insulating elements between the arc baffels to promote a series of small arcs thereby contributing to the increase in the arc voltage and ultimate extinguishment of the arc. All of these methods or apparatus of arc extinction involve additional parts adding to the manufacturing and maintenance costs of the circuit breaker as well as to the complexity of the circuit breaker.
Thus, there is a need for an arc extinguishing apparatus or arc chute that will extend and cool the electric arc formed during separation of circuit breaker contacts, while under load, without pneumatic or electro magnetic elements. There is a further need to provide an arc extinguishing apparatus with a minimum of unique elements. There is also a need for an arc extinguishing apparatus that can be used with several types of circuit breakers, such as circuit breakers with a single moveable contact element, with two moveable contacts as well as with single and multiple pole circuit breakers.